Safety-stop.



L. R. PALMER.

SAFETY STOP.

APPLICATION FILED JAN. 30,1911. 1,099,523 1 2. Patented June 9,1914.

2 SHEETS'SHEET 1.

FIGJ, 16 R? iZB 2 4 15 a WITNESSES:

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L.R.PALMERF SAFETY STOP. APPLIGATION PILED JAN.30, 1911. 1,099,512. Patented June 9,1911;

2 SHEETS-SHEET 2.

mygw HG-MRMIME UNITED STATES PAEFENT oriucn.

LEW RUSSELL PALMER, PITTSBURGH, PENNSYLVANIA.

snrE'rY-s'ror.

To all whom it may concern:

Be it known that I, LEW RUSSELL PALMER, residing at Pittsburgh, in the county of A1- legheny and State of Pennsylvania, a citizen of the United States, have invented or discovered certain new and useful Improvements in Safety-Stops, of which improvements the following is a specification.

In the operation of cranes and other forms of load-handling apparatus, which obtain motive power from electric motors, there are occasions when the operator for one reason or another permits the load to be carried to such height that it abruptly strikes some portion of the crane structure, frequently causing the load to be dropped upon men working beneath the crane.

It is the object of my present invention to provide a simple positive and effective means for stopping at a predetermined point the rising of loads thus carried, such stopping means being beyond the control of the operator, and its operation being independent of any external motive force.

In the accompanying drawings, which form a part of my specification, and in which I have illustrated my invention, Figure 1 is a plan view of a preferred form of circuit changer; Fig. 2 is an elevation of the circuitchanger shown in Fig. 1; Fig. 31s a sectional view taken on line IIIIII of Fig. 2; Fig. 4 shows diagrammatically in full lines the wiring system employed in the practice of the invention when the motor is running normally; Fig. 5 is a view similar to Fig. 4,.showing in full lines the wiring system employed when the motor is operated as a brake; Fig. 6 is a plan view of a modified form of circuit-changer; Fig. 7 is a sectional view taken on the line VII-VII, Fig. 6; and Fig. 8 is an elevation showing my invention in its adaptation to a hoisting crane.

Like numerals refer to like parts in the several figures.

Since the hoisting crane of itself forms no part of my invention, only such parts as at feet my invention are shown.

Referring to Fig. 8, an idler 5 is shown, rotatably mounted between a pair of hori zontal channels 6 (one of which -is not shown), which form part of the structural body of the crane trolley. The cable 4 passes over the idler 5 and around the pulley block 7 to a suitable drum {not shown), operatively connected to the hoisting motor, so

Specification of Letters Patent:

Application'filed January 30, 1911.

Patented June 9, 1914.

Serial No. 805,561.

that as. the drum rotates in one direction or the other, the pulley-block 7 will be raised or lowered with whatever load may be attached thereto.

When it is necessary to hoist a load to a considerable height, so that it may pass over the top of whatever may be along the line of its intended transfer, there is danger, usually due to the carelessness of the operator, of hoisting it too far, thereby bringing the pulley-block 7 abruptly against the channelbeam 6, which may cause a rupture of the cable or otherwise bring about the dropping of, the load. To guard against this overhoisting I place a circuit-changer 8 in circuit with the motor, which will be efiective when the load has been raised to a predetermined point to open the main circuit and complete a short circuit in series through the field and armature of the motor, as hereinafter described, sothat the motor will change itself to a generator, the momentum of the armature (and whatever shafts and Wheels are connected thereto) being the mechanical energy operative to turn the armature against the lines of force set up by the magnetized field. It will be readily understood by those skilled in the art, that when this short circuit has been m tablished, the armature will be brought to a stand-still very quickly, since its continued movement is resisted by the lines of force of the field, which lines of force are proportional to the current induced by the rotation of the armature, the current in turn being proportional to the speed of rotation of the armature.

I do not wish to limit myself to any particular form of eircuit-changer, as various forms will adapt themselves to different installations and accomplish the desired end. As shown in Figs. 1, 2 and 8, my preferred form of circuit-changer is mounted upon the sheave-carrying channels 6 and is conveniently made of a stationary part and a mov.--

able part with a suitable trip-lever device. The stationary part consists of a mounting plate 9, upon which an insulating board 10 is suitably mounted. To the insulating board I attach four pairs of contact pieces, preferably of brass, provided with wiring connections, and disposed between the con tactors there are insulation blocks rising to the level of the top of the contactors. Two pairs of these contact pieces R and R are in use when the crane is running in its non shown, for, obviously, many forms will suggest themselves to those skilled in the art. As shown in Fig. 3, the bridge consists of a casing 26, which is secured to the shaft 11 and loosely surrounds two carbons 23,

which carbons are conveniently held against.

the contactors by a spring 24: acting against a two-lugged member 25, which is preferably of brass. It will be understood that the current passes from one contactor B through a carbon 23, the two-lugged member 25, the second carbon 23 into the second contactor R and that the bridges are properly insulated to insure this conduction of the current. The said shaft and bridges are supported, as shown in Fig. 2, by angles 13 and 13*, which are secured to the mounting plate 9. The shaft 11 is further pro-' vided with a spring 14 and a collar 15, the spring loosely surrounding the shaft, and the collar being secured thereto. The arrangement of the spring 14, contact bridges 12 and 12 collar 15, and supports 13 and 13 is such that,-When the contact bridges are completing the circuit through the contact pieces R and R the. spring is compressed between the support 13 and the laterally extending portion of the bridge 12, y

and that, when the trip lever which holds the spring in its compressed condition is released, as hereinafter described, the spring will rapidly push the shaft toward the support 13, the movement being limited by the collar 15 striking against the last named support. In this second position the bridges 12 and 12 will complete electrical connection'between the-pairs of contact pieces B and B respectively.

As heretofore stated the bridges are held in position over the running contactors,

against the resistance of the spring, by a trip lever. Various forms of trips suitable for different installations of my device will suggest themselves to those skilled in the art. conveniently fulcrumed at 17 to a downwardly projecting frame'lS. A spring 19 keeps the lever in its normal position, and a flexible cord 20 is attached at one end to the lower arm of the lever 16 and at the other end to a second downwardly projectmg frame 21, in such position that the As herein shown, the triplever 16 is pulley block 7 or some attachment thereto, will strike the cord, and hence trip the lever, before the danger point is reached. The upper arm of the lever 16'engages a slotted lug 22, which is secured to the shaft 11, the arrangement being such that, when the lever is tripped, the lug will be disengaged and the spring will ,be effective tothe motor, the short circuit being independent of the; operating circuit and passing through the armature in a reverse direction to that of the operating circuit.

In Fig. l a suitable wiring system for the hoisting apparatus is diagrammatically shown, and in Fig. 5 a wiring system for the braking action is similarly shown. In Fig. 4 the wires are shown leading to and from a suitable controller. C, each wire being indicated by the initial letter ofthe part to which it leads. The controller C receives the current at L and bridges it to F, from whence it flows along the line successively through a solenoid S, (the use of which, to control a friction brake, is well known in the art), field F of the motor,.points F and A of the controller, running-contactors R, armature A of the motor, running-contactors R and out the line Wire L. It will be understood that the current flows as indicated by virtue of the fact that electrical connection is not established between the pairs of brake contactors B or B so that the only possible avenue of How is through the running-contactors R and R When the lever 16 has been tripped and the circuit-changer has changed electrical connction from the running to the brake-contactors, it will be seen that the main line circuit will be broken, and that a short circuit is established, as indicated in Fig. 5 through the field F, brake-contactors B, armature A, brake-contactors B and resistance K, which may be placed in the short circuit to reduce the strength of the current generated and hence diminish the intensity of the dynamic braking action of the motor. It will be observed that in this short circuit the current may flow through the field in the same direction as before the braking circuit was established, and the armature current may flow in a reverse direction.

Referring to Figs. 6 and 7 I show a second or alternate form of circuit-changer, wherein there is a bridge for each pair of contactors, and wherein the bridges are mounted upon a rotatable shaft which is Ill yieldingly held, by the trip-lever l6 acting against the spring 14, in a position such as to complete the main circuit. In this construction the bridges 12 and 12 close the running circuit through the running contactors R and R, and when. the lever is tripped, the shaft is turned by the spring 14, so that the bridges 12 and 12 will close a short circuit through the brake contactors B and B in the manner heretofore described. The arm 22 is mounted on the shaft so that it will limit the rotation of the shaft to whatever may be the angular displacement of the bridges, which displacement in this case is 90, so that the arm 22 passes through an arc of 90 before it strikes the mounting plate 9". Also the bridges as well as the contactors are properly insulated from each other and their supports. The other details of my alter nate construct-ion will be apparent from the description of my preferred form.

It will be observed that, when the circuitchanger has moved to'open the circuit established through the running-contactors, and completes a circuit through the brakecontactors, the armature and field of the motor will be connected in series, the circuit through the armature being reversed. During the interval of change, the field-magnets do not become demagnetized, so that the continued rotation of the armature (due to the momentum) will be resisted by the lines of force of the field, and such resistance will induce a reverse current in the armature. This induced current, being in series circuit with the field, will increase the magnetization of the field and; hence add to the resistance to the armatures rotation. It will'be seen that, by this operation, the rotation of the armature will be quickly overcome, and that the load will not rise to any substantial height above the predetermined point.

It will be seen of my invention that the stopping of the load at a predetermined point will be effected rapidly, that the stopping means are entirely beyond the control of the operator and that the dynamic breaking is effected independently of the mainline current.

I claim as my invention:

1. In a hoisting apparatus, the combination of a movable load-engaging member, a motor effective to operate said member and having a series field winding, an operating circuit for said motor, a manuallycontrolled controller for the motor in the operating circuit, means, for opening the operating circuit and connecting the armature and series field in closed circuit with the said armature connections reversed, said means being inde endent of said controller and effective w en said movable member reaches a predetermined point in its travel.

2. In a hoisting apparatus, the combination of a movable load-engaging member, a motor effective to operate said member andhaving a seriesfield winding, an operating circuit for said motor, a manuallycontrolled controller for the motor in the operating circuit, a two-position circuit changer independent of said controller and adapted when in one position to'close the operating circuit and when in its alternate position to open the operating circuit and connect the armature and series field in closed circuit with the armature connections reversed, and means lying in the path of said load-engaging member for shifting said circuit changer to its said alternate position.

3. In a hoisting apparatus, the combination of a movable load-engaging member, a motor effective to operate said member and having a series field Winding, an operating circuit for said motor, a manually-controlled controller for the ,motor in the operating circuit, means for opening the operating circuit and connecting the armature and series field in closed circuit with the connection to one of said motor elements reversed, said means being independent of said controller and effective when said movable member reaohes a predetermined point in its travel.

In testimony whereof I have hereunto set my hand.

LEI V RUSSELL PALMER.

Witnesses PAUL N. CRITCHLOW, ALICE A. TRILL. 

